The prescriptions of the generalized interaction current in Eq. (REF ) and the auxiliary current \(C^\mu \)  in Eq. (REF ) ensure that the full photoproduction amplitude of Eq. (REF ) satisfies the generalized WTI and thus is fully gauge invariant [1]}, [2]}, [3]}, independent of what particular forms are chosen for the phenomenological form factors \(f_s\)  and \(f_t\) .
